Method of treating complex leadzinc ores



June 20, 1944. C WOOD 2,351,795

METHOD OF TREATING COMPLEX LEAD-ZINC ORE Filed Feb. 13. 1943 LL, ,6 4L

C/vA/H 5 0. W000 INVENTOR.

Patented June 20, 1944 Charles D. Wood, Huntington Park, Calm, as-

signor to Los Angeles Chemical 00., Los Angeles.

Callh, a corporation of California Application February 13, 1943, SerialNo. 475,722

3 Claims. (Oi. 75-120) The present invention pertains to a method oftreating ores containing lead and zinc, for the purpose of permittingready separation of these two metals from the ore. Ores containing leadand zinc in admixture exist in very large quantities and althoughtremendous amounts of these has not been used because of the diillcultyheretofore encountered in separating zinc-from lead,

and vice versa. Zinc contaminated with lead is metals are available inthis form of ore, the ore not adapted for many of the uses to which zincis Put and lead contaminated with zinc is unsuited for many uses otherthan paint pigment. Even for the latter purpose the manufacturers ofpaint pigments desire a ratio of approximately five times 2:3 much zincas lead in the mixture. 1 V

The lead and zinc ores contain these metals in the form or carbonatesand sulfides. Separation of the metals from the ore is rendereddifficult in many causes due to the fact that the slagging point of theore is lower than the reduction point.

The present invention is directed to a simple and effective method oftreating these complex ores so as to permit the ready separation of leada by-product of the magnesium metal inclustr,,

in the treatment of lead-zinc ores.

These and other objects, adaptations, advantages and uses of the presentinvention will become apparent to those skilled in the art from thefollowing description of the process. In order to facilitateunderstanding, reference will be had to the appended graph whichdiagrammatically illustrates exemplary forms of devices which may beusedand the steps of the process.

As previously stated, lead-zinc ores generally contain zinc and leadeither. as a carbonate or sulfide. The gangue with which these metalcompounds are associated may vary extensively in composition, althoughin many instances these lead-zinc ores are found in dolomitic formationsso that calcium and magnesium occur in relatively large amounts. Theores may also contain appreclable quantities of iron, many of themcontalning from about 6% to as high as 10% or 12% of iron.

from the zinc and at the same time from whatever iron is customarilypresent in such ores.

Generally stated, the invention contemplates roasting the ore to convertthe lead and zinc comhounds into oxide and then subjecting the finelyground roasted ore to the action of anaqueous medium containing causticsoda so as to form soluble lead and zinc compounds. The gangue orinsoluble compounds are then removed by filtration, sedimentation or thelike and the soluble lead compounds oxidized and precipitated Irom thesolution. After removal of the oxidized lead compounds, the remainingsolution is treated for the precipitation and removal of zinc therefrom.

An object of the present invention, therefore, is to disclose andprovide a method of treating ores containing lead and zinc fortherecovery of these metals therefrom.

A further object of the invention is to disclose and provide arelatively simple and eflective method of removing lead and zinc asseparate metal compounds or metals fromiores containing. these metals inadmixture. A still further object of the invention is to dis-' close andprovide a mode of treating lead and zinc ores whereby soluble metalcompounds are formed and the lead then precipitated therefrom.

Again, an object of the present invention is to disclose a processcapable of utilizing the exces- The present invention is particularlywell adapted for use in localities where large quantities of causticsoda are available. Since the process does not require concentratedcaustic soda solutions, the liquor from electrolytic chlorine cells,generally containing about 8% to 10% 01' sodium hydroxide and 10% to 12%sodium chloride, may be used.

The following description exemplifies the steps which may be carried outin accordance with the invention.

The lead-zinc ore may be-crushedin any suitable crusher I to a sizeadapted for roasting. The a size or mesh oi. the ore may be varied,depending upon the type or roasting equipment employed.

Ordinarily, crushing the ore so-asto pass a 1 inch mesh is sufllcient.The ore is then roasted in any suitable equipment, such as for example,the rotary kiln 2, for the purpose of reducing the ore, andparticularlythe zinc and lead compounds therein, to the form of oxides.-Galena,

PbB, is oxidized in this manner to PbO; the zincand lead carbonates arealso oxidized to PhD and 2:10. Obviously other reactions maysimultaneously take place but since they do not materially sivequantities of caustic soda. made available as so aflect the ultimateresult, they will not be describedlndetail.

. The roasted ore is then preferably ground to a state of line divisionand brought into contact with an aqueous medium containing caustic soda.

Although the ore may be first ground to a state oi ilne division, say topasse. 16 or 20 mesh sieve, and then brought into contact with the Vcaustic soda solution, the appended flow chart between the solution andthe ore,

' charge the unreacted (which contains t e shows this line grinding astaking place in a ball or tube mill 3, which is supplied with theroasted ore and with a relatively small quantity of caustic sodasolution through a line 4. Wet grinding is thus accomplished in the ballor tube mill 3 and a more intimate and rapid reaction is thus attained.

The ground roasted ore may then be distributed as by means of a conveyor5 into suitable boiling or leaching tanks 8, 6, etc. Additionalquantities of solution containing sodium hydroxide may be supplied tothese tanks as by line 1. Each of the tanks may be provided with heatingmeans such as for example, suitable coils supplied with steam. Thereaction between the canstic soda and the ore is facilitated by the useof high temperatures, the order of 180 F. to about 220 F., but it is tobe understood that the invention is not limtied to the use ofsuperatmospheric temperatures since lower temperatures may be employed.The use of lower temperatures, temperatures, requires greater time ofcontact but the same reactions willtake place.

In the event caustic solutions from electrolytic cells are available,said solutions may be supplied to the tanks 6 through the line 1 inquantity suilicient to form soluble lead and zinc compounds.- Relativelydilute solutions of sodium hydroxide may be employed andthe presenceofsodium chloride in the solutions is not detrimental since the sodiumchloride remains as an inert ingredient. Solutions ranging from 6% toabout 12% sodium hydroxide may be employed although more concentratedsolutions will react more rapidly. For commercial operation it is notnecessary to use concentrations in excess of about 20% sodium hydroxide.

The reactions which take place in the tanks t may be represented asfollows: I

, quired to convert the lead and zinc into the soluble sodium compoundsthereof. However, it has been found that some forms of sodium silicateare also formed in small amounts.

After the reaction has been completed, the contents of the tanks may bepassed by suitable conduits, such as i, to means for separating solidsfrom liquids. Although sedimentation tanks may be used. continuous typefilters have been found satisfactory. The appended diagram illustratesthe continuous filters 9 and 8' adapted to dissolids or gangue to asuitable point of disposal, the solutions being then that is,temperatures on such as atmospheric 'soda solution to sodium sent as byconduits II to suitable tanks It for the precipitation of lead from thesolution.

The separation of lead from the solution sodium salts of lead and zinc)canbe most readily eflected by passinl chlorine through the solution.For example, the

tank ll may be provided with suitably perforated distribution coilssupplied with chlorine byline ii. The odium plumbite is decomposed bythe chlorine into sodiumchloride and lead oxide. The chlorination shouldbe carried out with chlorine suiiicient to decompose the sodium plumbitebut insumcient to form zinc chloride. Zinc ch10;

reaction which ride will not form, however, until substantially all ofthe lead compound has been oxidized into lead oxide. The temperatureduring the chlorinating step may range from atmospheric to temperaturesof the order of 1". The use to which the resulting lead oxide is put mayinfluence the temperature at which the chlorination is carried out inceyellow lead oxides are formed at or redder lead oxides are formed athigher temperatures. The precipitated lead is not as colloidal inparticle size when higher temperatures are employed during calcination.

After the lead has been precipitated in the form of oxides as describedhereinabove. the suspension may be discharged as by line ll into acontinuou filter l4 and the precipitated lead oxides filtered off. Theremaining solution containing sodium zincate is discharged from thefilter I by line II and sent to tank l6. This tank is used inprecipitating zinc in the form of a carbonate. which is most readilyformed by bubbling carbon dioxide gas through the solution in tank ll,carbon dioxide being supplied by line II to a suitable spray head,perforated distribution pipe, or the like. The reaction taking place intank ll may be represented as follows:

Upon precipitation of the zinc carbona e in the manner described, thesolution may be di charged from tank It by line it to filters II, thezinc carbonate being separated from the residual liquid. This residualliquid discharged by line Ill may be used in cyclic operation of theprocess or for other purposes.

It is to be noted that the carbon dioxide used in carbonation mayconsist in large part of stack gases derived from the roasting operaton. It is also to be noted that although the slurry is preferably heatedin the digestion tanks 0. the solution of. the soluble zinc and leadcompounds should be at a lower temperature during oxidation of the leadcompounds into lead oxides Cooling, although not illustrated in theappended diagram; may take place either by the use of suitable storagetanks and lapse of, time or by the use of spray ponds. During theoxidizing takes place in tanks ll, an excess of caustic should bepresent. The reaction which takes place when chlorine is used is notwell understood and it may, well be that the chlorine forms sodiumhypochlorite which in turn causes the decomposition of the sodiumplumbite.

The products obtained. namely, and zinc carbonate, are of sumcientlyhigh to be readily adapted for use as sources for the pure metals leadand zinc, or for the many other uses to which these metallic compoundsare suited. The zinc carbonate may be used as such for some purposes orit may be roasted to form zinc oxide. In addition, attention iscalled tothe fact that the vgangue obtained in the first separating setp is alsoof commercial importance. Most lead-zinc ores contain silver and othermetals and although the original ore may contain silver in such smallquantities that the recovery of silver therefromis not commerciallyeconomical, the gangue obtained by the treatoxides of lead ment of thepresent inventioncontains the silver silver and other metals therefrom.

lower temperatures and the darker p ty It is to be understood thatnumerous changes and modifications may be made. The steps of washing theprecipitated products during filtration or subsequent to such filtrationhave not been specifically referred to but all changes and modificationscoming within the scope of the appended claims are embraced thereby.

I claim:

1. A method or treating ores containing lead and zinc in the form ofcarbonates and sulfides, comprising: roasting the ore to convert leadand zinc therein into oxides: subjecting the roasted' fides, whichcomprises: roasting the ore to con- 25 vert lead and zinc therein intooxides; grindin passing chlorine gas through the roasted ore to a state01 fine division in the presence of an aqueous solution containingcaustic soda; subjecting the ground roasted ore to the action ofadditional aqueous med um containing caustic soda to form sodiumplumbite and sodium zincate; removing insoluble matter from g thesolution; passing chlorine through the solution in quantity .suflicientto convert sodium plumbite into lead oxide: separating the precipitatedlead oxide from the solution; then car bonating the remaining solutionto form zinc carbonate and separating the zinc carbonate from theresidual solution.

3. In a method of treating alkaline aqueous 15 solutions containingsodium plumbite and sodium zincate obtained by digesting lead-zinc oreswith sodium hydroxide solutions, the steps of removing insoluble matterfrom the solution; passing chlorine through the solution in quantity 20sumcient to convert sodium plumbite into lead oxide; separating theprecipitated lead oxide from the solution; then carbonating the remainving solution to form zinc carbonate; and separating the zinc carbonatetrom the residual solution.

CHARLES D. WOOD.

